WO2011154636A1

WO2011154636A1 - Method for preventing the pumping of an engine turbocharger

Info

Publication number: WO2011154636A1
Application number: PCT/FR2011/051187
Authority: WO
Inventors: Virginie Seigeot; Cyril Peronnet; Olivier Tanneau; Thierry Martin; Manuel Tancrez; Bertrand Dreyer; Patrick Bey; Jean Filipe; Guillaume Lefranc
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2010-06-11
Filing date: 2011-05-25
Publication date: 2011-12-15
Also published as: FR2961263A1; EP2580456A1; FR2961263B1

Abstract

The invention relates to a method for preventing the pumping of an engine turbocharger, said method including: detecting an instantaneous torque of the engine, said torque corresponding to an injection of a first fuel flow; and detecting a drop in engine torque requirement in a torque less than the instantaneous torque of the engine. The method is characterized in that it includes the gradual cutoff (762) of the fuel flow injected once the drop in torque requirement is detected. The invention also relates to a power train implementing the method and to a vehicle having the power train.

Description

METHOD FOR PREVENTING PUMPING OF A TURBOCHARGER

OF AN ENGINE

The present invention claims the priority of the French application 1054619 filed June 1, 2010 whose content (text, drawings and claims) is here incorporated by reference.

[Ooo2] The invention relates to a method for preventing the pumping of a turbocharger. The invention also relates to a powertrain and a vehicle implementing such a method.

[ooo3] In the automotive field, the engines are supplied with air to achieve the combustion or the explosion of fuel in the cylinders. Motor vehicles then comprise an air loop 80 such as that shown in FIG. The air loop then typically comprises an air filter 82 for the entry of atmospheric air for combustion, a turbocharger 84 for the compression of air, a tube 86 for the circulation of air to metering device 88. The metering device 88 assures the metering of the amount of outside air that will be combusted in the engine 94 as a function of the flow of fuel injected into the engine 94. The engine 94 produces exhaust gases which drive the turbocharger 84 in order to benefit from the kinetic energy of the exhaust gases to compress the atmospheric air not yet burned. Once the kinetic energy of the exhaust gases has been recovered, the exhaust gases are discharged into an exhaust line which may comprise a particulate filter 78. The air loop 80 may be completed by a bypass for a cooler of air on admission 90 (noted abbreviated RAS) and by an exhaust gas recirculation bypass 98 (noted abbreviated EGR for exhaust gas recirculation in English). A manifold 96 then brings part of the exhaust gas to the outlet of the engine 94 to the distributor 92 upstream of the engine 94.

[Ooo4] In known manner, the turbocharger is subject to a pumping phenomenon which can be detrimental to the comfort of the user of the motor vehicle. [0005] FIG. 2 illustrates a sectional view of the blades 20 of a wheel of the compressor 84 with a flow of incident atmospheric air 30. The pumping of the compressor 84 is initiated by a variation of the flow at the blades 20 of the compressor. This variation of the air flow 30 in contact with the blades 20 is capable of forming a delamination 32 of the boundary layer. This detachment 32 leads to a restriction of the passage section between the two blades 20 and therefore to a sudden reduction in the flow of air flowing in the compressor 84. By coupling the compressor with the exhaust gas, the variation of the flow rate of the compressor 84 causes a variation of the engine speed, which in turn causes a variation in the flow rate of the compressor. This coupling can then cause an oscillation of the air flow upstream and downstream of the compressor 84 which generates the characteristic pumping noise (corresponding to "barking"). Eventually the pumping phenomenon can also cause damage to the bearing system of the compressor wheel. Such damage to the bearing can lead to engine operation on part of the bearing lubrication oil (known as the oil start), which is detrimental.

FIG. 3 shows the diagram of the various speeds in the context of the system consisting of the air flow 30 and the blades 20. The speed U referenced 24 corresponds to the speed of rotation of the wheel. According to the incident speed (C, referenced 38) of the air flow, the flow rate of the flow (W, referenced 36) of the air in the compressor 84 is related to the angle of incidence 34 of the flow of air.

[ooo7] Thus the appearance of the pumping phenomenon is related to various factors among which we find a bad sizing of the aerodynamics of the wheel of the compressor 84 or the modification of the angle of incidence 34 of the flow of atmospheric air on the blades 20, or the variation of the air flow circulating in the compressor 84. The various factors of pumping can cause two operating situations involving pumping, as shown in Figure 4. On the one hand the pumping 60 may result from a static bias 40. The aerodynamics of the wheel 44 and the variations the angle of incidence of the flow (represented by the suitability flow upstream / wheel 42 ) causes a static load 40.

[ooo9] On the other hand the pumping 60 may result from a dynamic solicitation 51. The dynamic bias 51 corresponds to a variation 52 of the flow rate of the compressor 84, denoted by Qcomp.

[ooi o] In all cases, the pumping ultimately causes air flow oscillations with transmission phenomena or damping possible oscillation 62 of the compressor flow. By recovering the kinetic energy of the exhaust gas at the output of the engine 94, a coupling 64 of the compressor 84 and the air loop 80 can maintain the pumping of the compressor 84.

FIG. 5 illustrates, in a plane of pressure with respect to the flow rate of the compressor, the pumping phenomenon of the compressor 84 with a dynamic stress. The curves 79 show the operating curves of the iso-power turbocharger. After a stable operation of the compressor at point 58, a sudden reduction of the compressor flow occurs. The compressor 84 then passes to point 56 with a large variation in flow with respect to the variation of the pressure. The compressor 84 is then driven dynamically in oscillations 54 with a maintenance of oscillations of the air flow by the response of the whole system.

Furthermore, FIG. 5 also illustrates the limit curve 48 for static pumping beyond which the compressor enters pumping without variation of the air flow of the compressor 84. Thus, when the air flow of the compressor is too low with high pressure, the conditions are met for the compressor 84 to come into pumping.

The graph of Figure 5 comprises the ordinate PiC report of the downstream pressure (P2) of the compressor 84 on the upstream pressure (P1) of the compressor. The graph comprises on the abscissa the corrected flow rate (Qcorr) of the compressor 84, obtained according to the formula:

where P ₀ , T ₀ , Ro respectively correspond to the pressure, to the air temperature and the constant of the ideal gases of the air at the moment of the characterization of the compressor 84 and where P _re f, T _ref , R _ref correspond respectively to the pressure, the air temperature and the ideal gas constant of the air under normal conditions of temperature and pressure (ie 298 ° K and 1 bar)

Two operating hypotheses can cause dynamic loading of the compressor 84.

According to a first hypothesis, the opening of the EGR bypass causes the replacement of a portion of the atmospheric air supplied by the compressor 84 by exhaust gas. Thus, when the engine speed is maintained, the need for atmospheric air is lower, which results in a decrease in the air flow rate in the compressor 84. This decrease in air flow can dynamically urge the compressor 84 into pumping.

According to a second hypothesis, the air flow of the compressor 84 is directly reduced by reducing the engine speed. This second hypothesis typically corresponds to the drop in torque demand to the engine, that is to say to a foot lift or release of accelerator pedal by the user of the vehicle comprising the engine.

Different approaches have been envisaged in the prior art in an attempt to avoid pumping the compressor 84.

Document US Pat. No. 6,196,189 proposes a filtering of the action setpoint on the air butterfly when the variations between the motor speed reference and the actual speed are too great. The document US 2004 216457 proposes in the field of locomotives, to act on the speed of the engine in case of detection of compressor pumping. US 6 105 555 proposes an action on the exhaust valve so as to increase the exhaust gas flowing in the turbocharger to solve the problems of pumping the compressor. However the proposed solutions do not provide full satisfaction in solving the problem of pumping the compressor.

There is therefore a need for a method preventing the formation of the turbocharger pumping.

For this, the invention provides a method for preventing the pumping of a turbocharger of an engine comprising:

detecting an instantaneous torque of the engine corresponding to an injection of a first fuel flow;

detecting a torque demand drop of the motor at a torque less than the instantaneous torque of the motor;

the method being characterized in that it comprises the progressive cutting of the injected fuel flow as soon as the torque demand drop is detected.

According to one variant, the progressive shutdown of the fuel flow causes the reduction of the compression ratio of the turbocharger and the reduction of the turbocharger flow rate.

According to a variant, the progressive shutdown of the fuel flow is maintained for a predetermined time, preferably greater than or equal to 0.5 seconds.

According to one variant, the progressive shutdown of the fuel injection flow rate is achieved by injecting an additional fuel mass at the fuel flow rate corresponding to the requested torque drop.

According to a variant, the additional fuel mass is calibrated according to at least one of the following characteristics:

- the engine speed;

the desired torque by the user of the engine;

- the steering situation of the gearbox.

According to one variant, the gradual shutdown of the injected fuel flow comprises: a first phase with a first constant rate of cutoff of the injected fuel flow as soon as the torque demand drop is detected;

a second phase with a second constant rate of cutoff of the injected fuel flow, following the first phase, the second cutoff speed being lower than the first cutoff speed;

a third phase with a third constant rate of cutoff of the injected fuel flow, following the second phase, the third cutoff speed being greater than the second cutoff speed.

According to one variant, the progressive shutdown of the fuel injection is obtained by filtration of the fuel injection setpoint as soon as the torque demand drop is detected.

The invention also proposes a powertrain of a motor vehicle comprising an air loop with turbocharger, the powertrain being characterized in that it implements the method as described above.

According to one variant, the powertrain comprises a diesel-type thermal engine.

The invention also proposes a motor vehicle characterized in that it comprises the powertrain as previously described.

Other features and advantages of the invention will appear on reading the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show:

• Figure 1, a diagram of an engine air loop with turbocharger;

• Figure 2, a sectional view of the blades of a wheel of the turbocharger compressor;

• Figure 3, a diagram of the different speeds in the system formed by the air flow and the compressor;

• Figure 4, a logic diagram of the various factors causing the compressor to pump; • Figure 5, a graphical representation of the phenomenon of compressor pumping in the pressure plane compressor flow;

• Figure 6, a strategy of gradual shutdown of the fuel flow following the detection of the torque demand drop;

FIGS. 7A and 7B, the evolution of the various magnitudes of the powertrain in the absence of the proposed pumping prevention method;

• Figures 8A and 8B, the evolution of the different magnitudes of the powertrain with the application of the proposed pumping prevention process.

The invention relates to a method for preventing the pumping of a turbocharger of an engine. The method includes detecting an instantaneous torque of the engine corresponding to an injection of a first fuel flow. The method further includes detecting a torque demand drop of the motor at a torque less than the instantaneous torque of the motor. This fall may correspond to the case of lifting of the foot of the user of the motor vehicle including the engine. Upon detection of the drop in torque demand, the proposed method includes the gradual shutdown of the injected fuel flow.

Such a situation corresponds to a spinning as illustrated in FIG. 6. FIG. 6 represents in fact the evolution of the instantaneous engine torque (CMI) as a function of time with a strategy of progressive shutdown 76 of the fuel flow rate. upon detection of the torque demand drop and a cut strategy referenced 760.

The gradual decrease in fuel flow induces a gradual and constant change in fuel flow. This also induces a control of the engine speed drop (Nrpm) and therefore of the engine air flow (Qmot). This is particularly related to the formula: c _vl ^ rdt _ vol

R * T2 " ^cyl 120 where Vcyl corresponds to the volume of the engine displacement 94 and rdt_vol corresponds to the volumetric efficiency. In the absence of a sharp drop in the air flow of the motor 94, the air flow of the compressor 84 is gradually decreased.

Moreover, this gradual decrease in fuel flow allows the turbine to recover an enthalpy at the foot drop which has the effect of maintaining the speed of the turbocharger and the PiC.

These combined effects then allow to suppress the compressor pumping.

Thus the proposed method prevents the formation of pumping turbocharger.

By application of the method can be obtained a power train with the engine 94 and turbocharger 84 preceding preventing the pumping of the turbocharger 84. The method is preferably used with a powertrain comprising a diesel engine thermal motorization because of the widespread use of turbocharger with diesel engine. A motor vehicle comprising such a powertrain is then advantageous.

FIG. 5 illustrates the zone 50 of dynamic loading in which the compressor enters into pumping due to the variation of the air flow rate. Thus the operating ranges likely to present dynamic pumping by falling engine speed can be defined by:

• a Nrpm engine speed of between 1000 and 2500 revolutions. min ^"1 ;

A compressor ratio PiC of between 1 and 3;

• a request for a drop in engine speed from -50 to -3000 revolutions. min ^"1. s ^{" 1} .

The proposed method corresponds to the path 72 which allows to stay away from the zone 50. The proposed method causes the reduction of the compressor compression ratio of the turbocharger and the reduction of the turbocharger compressor flow such as illustrated. Another possible strategy corresponds to the strategy 74 with an increase of the air flow during the reduction of PiC. According to FIG. 6, the requested torque drop corresponds to the passage of the torque at the level 768. The fuel injection is then maintained so that the engine torque progressively passes from the first engine torque level to the level 768. The maintenance of the fuel injection corresponds to the injection of an additional fuel mass to the fuel flow corresponding to the level 768. This additional fuel mass is calibrated preferably calibrated according to:

• engine speed;

The desired torque of the vehicle user;

• the steering situation of the gearbox.

The gradual shutdown of the injected fuel flow may comprise several phases. In a first phase, a first constant rate of cutoff of the injected fuel flow is applied as soon as the torque demand drop is detected. This first phase corresponds to the portion 762 of the strategy 76. This makes it possible to avoid pumping. In comparison, strategy 760 proposes, during this first phase, first a sudden cut in fuel flow, which is generating a pumping situation.

In a second phase, a second constant rate of cutoff of the injected fuel flow is applied following the first phase. This second phase corresponds to the portion 764 of the strategy 76. The second cutoff speed is chosen lower than the first cutoff speed.

In a third phase, a third constant rate of cutoff of the injected fuel flow is applied after the second phase. This third phase corresponds to the portion 766 of the strategy 76. The third cutoff speed is chosen greater than the second cutoff speed.

Furthermore, the gradual shutdown of the fuel injection can be obtained by filtration of the fuel injection setpoint upon detection of the torque demand drop.

Figures 7A to 8B correspond to tests showing the relevance of the proposed pumping prevention method. Figures 7A and 7B show the evolution of different magnitudes of the powertrain when the proposed pumping prevention method is not used. Qair (referenced herein 602) corresponds to the air flow of the compressor 84. Qcarb (referenced herein 606) corresponds to the fuel flow injected. At the occurrence of a drop in the engine speed 604, that is to say during the torque drop 608, the compressor 84 enters pumping. The pumping of the compressor 84 is notably visible by the oscillations of the engine speed 604.

Figures 8A and 8B show the evolution of the different magnitudes of the powertrain when the proposed pumping prevention method is applied. Qair (referenced herein 702) corresponds to the air flow of the compressor 84. Qcarb (referenced herein 706) corresponds to the fuel flow injected. At the occurrence of a 708 decrease of the engine speed 704, that is to say during the torque drop 608, the fuel flow 706 is cut progressively. The compressor 84 then does not pump. It may be preferred to provide a gradual shutdown of the fuel flow for a time greater than or equal to 0.5 seconds as in the case shown in Figures 8A and 8B.

Claims

A method of preventing pumping of a turbocharger from an engine comprising:

• the detection of an instantaneous torque of the engine corresponding to an injection of a first fuel flow;

• the detection of a drop in engine torque demand at a torque lower than the instantaneous torque of the engine;

the method being characterized in that it comprises progressively cutting (762) the injected fuel flow as soon as the torque demand drop is detected.

2. The method according to claim 1, characterized in that the progressive shutdown of the fuel flow causes the reduction of the compression ratio of the turbocharger and the reduction of the flow of the turbocharger.

3. The method according to claim 1 or 2, characterized in that the progressive shutdown of the fuel flow is maintained for a predetermined time, preferably greater than or equal to 0.5 seconds.

4. The method according to one of claims 1 to 3, characterized in that the progressive cutting of the fuel injection rate is achieved by injecting an additional fuel mass fuel flow corresponding to the fall of couple asked.

The method according to claim 4, characterized in that the additional fuel mass is calibrated according to at least one of the following characteristics:

• the engine speed;

• the torque desired by the engine user;

• the steering situation of the gearbox.

6. The method according to one of claims 1 to 5, characterized in that the gradual shutdown of the injected fuel flow comprises:

A first phase with a first constant rate of cutoff of the injected fuel flow as soon as the torque demand drop is detected; A second phase with a second constant rate of cutoff of the injected fuel flow, following the first phase, the second cutoff speed being lower than the first cutoff speed;

7. The method according to one of claims 1 to 6, characterized in that the progressive shutdown of the fuel injection is obtained by filtration of the fuel injection setpoint upon detection of the torque demand drop.

8. A power train of a motor vehicle comprising an air loop (80) with a turbocharger (84), the power unit being characterized in that it implements the method according to one of claims 1 to 7.

9. The powertrain according to claim 8, characterized in that the powertrain comprises a diesel-type thermal engine.

10. A motor vehicle characterized in that it comprises the powertrain according to claim 8 or 9.